Exhaust systems are widely known and used with combustion engines. Typically, an exhaust system includes exhaust tubes that convey hot exhaust gases from the engine to other exhaust system components, such as mufflers, resonators, etc. A muffler includes acoustic chambers that cancel out sound waves carried by the exhaust gases. Although effective, mufflers are often relatively large in size and provide limited noise attenuation.
It has been proposed to include a valve in the muffler to provide further noise attenuation. However, the proposed valves have numerous drawbacks that limit their widespread use in a variety of applications.
As known, the muffler is subjected to different operating conditions dependent upon application. For example, due to its usual position, a main muffler for a passenger car can be subjected to exhaust gases of 600 degrees Celsius, while mufflers used in truck, minivan or SUV applications are subjected to gas temperatures that can exceed 750 degree Celsius.
In passenger car applications, a passive noise attenuation valve has been directly incorporated within a muffler body to provide noise attenuation. This valve includes a spring for biasing a valve body for pivotable movement within a valve housing that defines an exhaust flow path. The spring has limited application in high temperature environments. Special high-temperature spring materials are often required, which can be very expensive. Also, these valves can be difficult to package in smaller sized mufflers, which are typically used as part of a multi-muffler configuration for larger vehicles such as trucks, SUVs, mini-vans, etc.
The valve controls exhaust flow rate along the exhaust flow path. The valve body is moveable between a closed position, where 100% of the exhaust flow path is blocked by the valve body, and an open position where blocking of the exhaust flow path is minimized.
Further, these known passive valves are used in a configuration where a by-pass flow path is provided. In this type of configuration, there is a primary flow path and a by-pass flow path for exhaust gases. The valve body is positioned within an internal muffler tube that defines the primary flow path. As discussed above, the valve body is configured to block 100% of the primary flow path when in the closed position. A by-pass tube is in fluid communication with the internal muffler tube at a position upstream of the valve body and at a position downstream of the valve body. Under certain conditions, such as when the primary flow path is 100% blocked for example, exhaust gases are directed around the valve body via the by-pass tube.
Providing by-pass flow paths is disadvantageous from an assembly, material, and weight perspective. Further, as discussed above, it is difficult to package these valves in smaller mufflers, and these valves are not able to operate effectively in high temperature environments.
Additionally, these known passive valve configurations do not effectively attenuate low frequency noise. Attempts have been made to improve low frequency noise attenuation without using passive valves by either increasing muffler volume or increasing backpressure. Increasing muffler volume is disadvantageous from a cost, material, and packaging space perspective. Increasing backpressure can adversely affect engine power.
Attempts have also been made to use a non-bypass configuration with an actively controlled, vacuum operated valve configuration. However, this is disadvantageous from a cost and packaging perspective.
Therefore, there is a need for a more effective noise attenuation valve that operates efficiently within the exhaust flow, and which can attenuate low frequency noise to provide a desired valve characteristic. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.